1. Technical Field of the Invention
The present invention relates generally to a dielectric resonator which may be employed within a higher harmonic range such as a microwave band, and more particularly to an improved structure which produces a dielectric resonator of compact size with low loss.
2. Background Art
In recent years, there is an increasing need for compact and lightweight portable terminal equipment in the field of radio communication. In particular, it is required to make resonators which will usually be bulky in radio communication devices, more compact and to enhance the performance thereof.
FIGS. 11(a) and 11(b) show a conventional dielectric coaxial resonator. FIG. 11(a) illustrates a vertical cross section of the coaxial resonator taken along the center line thereof. FIG. 11(b) is a side view.
The shown coaxial resonator generally includes a hollow dielectric substance 21, an inner conductor 22, and an outer conductor 23 to complete a quarter wave resonator structure wherein one end is open-circuited and the other end is short-circuited.
FIG. 12 shows a conventional microstrip transmission line resonator which includes a dielectric substrate 31, a microstrip transmission line 32 serving as a resonance element, and a ground conductor 33 to produce a half wave resonator structure with both ends being open-circuited.
The above prior art coaxial resonator has suffered from the drawback in that the unloaded Q as a performance index of a resonator is desirably high, but the resonator structure is bulky. Additionally, the prior art microstrip transmission line resonator also encounters the drawback in that the resonator structure may be thinned, but the loss is increased. Further, since the characteristic impedance of a transmission line is uniform and the length of the transmission line is one-quarter wavelength or half wavelength, higher harmonic resonance frequencies will be odd multiples or integral multiples of the fundamental frequency, thereby making it difficult to manufacture filters which are capable of suppressing higher harmonics.